1. Field of the Invention
The present invention is directed to a solenoid operated valve. More specifically, the present invention is directed to a two-stage solenoid valve for selectively providing a first and a second flow rate therethrough.
2. Description of the Prior Art
Prior attempts to provide two different flow rates have included the use of two valves in parallel flow lines with a selective actuation of the valves that have been provided with different size flow control orifices. Another prior art solution to the problem used a single orifice valve with a single coil and armature and a half-wave rectified alternating current (AC) input energizing signal. The energizing signal produced an oscillation of the armature at a fixed frequency to produce a reduced flow rate relative to a non-oscillatory fully opened position of the armature produced by a non-rectified energizing signal. Another prior art approach utilized a first and a second solenoid coil to respectively position a first and a second coaxial armature acting jointly on a single orifice sealing means to position the sealing means at a first and a second spaced position with respect to the orifice. These prior art approaches have inherent disadvantages such as chatter at reduced flow in the case of the oscillating armature, increased cost of the extra valve and plumbing in the case of the dual valve and inability to maintain a precise ratio between the two flow rates in the case of the valve using the dual armatures and single sealing means valve. Accordingly, in order to overcome the aforesaid shortcomings of the prior art, it is desireable to provide a valve having a selectively variable flow rate while exhibiting a quiet operation and precise selection of a flow rate to maintain a fixed ratio therebetween.